4 C H A P T E R   1 you know only English, you will not receive the message I am sending. If I am speaking Japanese grammar with English vocabulary, your understanding will also  be  seriously  impeded.  There  has  to  be  agreement  about  the  syntax  (the combination of the words), the vocabulary (the mapping between symbol and concept), and the semantics (the meaning of the vocabulary). RDF is a set of rules for creating semantics, and RDF Schema is a way of creating vocabularies. In practice, however, you rarely need to get that philosophical. You do have to recognize that classifications are necessarily arbitrary and that the names of concepts  are  inherently  meaningless.  Any  knowledge  representation  scheme will have to take this arbitrariness into account. Representing knowledge in a computerized format has been high fashion in the computer industry for a long time. Knowledge representation systems are an important  aspect  of  metadata,  but  they  have  a  big  inherent  weakness.  While they are mostly geared toward the scientific domain, they assume they are gen- eral, both in vocabulary and structure. Of course, they are not, and while they have come up with a lot of valid results in the field of intelligent agents, the work still suffers from the assumptions that there are universal ways of representing knowledge within one, centrally determined framework. This is most evident in the  classification  schemes  used  in  the  library  world.  Classifying,  as  they  do, information objects that represent anything, they do have presumptions to be general. But they are really specific, not in the least culture-specific. A library in Sweden is not classified in the same way as a library in the United States. RDF addresses this by providing for a decentralized scheme. Using the same structure, it allows anyone to create their own vocabulary. This enables you to take  the  good  things  from  the  artificial  intelligence  community  (intelligent agents and reasoning systems) and apply the good things from the Web (the transport  system,  the  data  representation,  the  decentralization  and  indepen- dence from a particular system). This intersection is the topic for this book. What Is RDF? RDF  is  a  format  to  make  assertions statements  that  are  intended  to  point something out. It has two roots: metadata and knowledge representation. The concepts do overlap, but the technologies which have been developed in the two fields, and the understanding of them, are very different. Library  communities  have  struggled  to  come  up  with  a  universal  format  for describing  books  that  can  be  used  in  electronic  catalogs.  The  result  is  the Dublin Core format (named after Dublin, Ohio, and not Dublin, Ireland). It is basically a set of attribute names and rules for which values they can take. The 69528_CH01Ix  4/6/2001 8:15 AM  Page 4